In recent years, a valve timing control apparatus capable of changing the opening and closing timing of an inlet valve and an exhaust valve in accordance with the operation status of an internal combustion engine (hereinafter also referred to as an engine) is in practical use. The valve timing control apparatus has a mechanism of changing the timing of opening and closing inlet and exhaust valves opened and closed in accordance with the rotation of the driven-side rotor by changing the relative rotation phase of the driven-side rotor with respect to the rotation of the drive-side rotor by actuation of the engine.
Generally, the optimum timing of opening and closing the inlet and exhaust valves differs according to the operation status of the engine such as at the time of starting the engine or at the time of running a vehicle. Accordingly, the relative rotation phase of the driven-side rotor with respect to the rotation of the drive-side rotor is constrained to a given phase between the most timing delay phase and the most timing advance phase at the time of starting the engine to thereby realize the optimum timing of opening and closing the inlet and exhaust valves. The valve timing control apparatus has a lock mechanism for constraining the relative rotation phase to the given phase.
As the lock mechanism provided in the valve timing control apparatus, for example disclosed in JP 2001-317314 A (Reference 1), there is the one in which a lock plate (corresponding to a lock mechanism of this disclosure) inserted into an outer rotor (corresponding to a drive-side rotor of this disclosure) is configured to be ejected and retracted in a radial direction of an inner rotor (corresponding to a driven-side rotor of this disclosure) and a torsion spring for biasing the lock plate to be pushed so that an end portion of the lock plate is fitted to a receiving groove (corresponding to a concave portion of this disclosure) is provided. In this device, the end portion of the lock plate is formed to be a shape tapered toward an end and a bottom portion of the receiving groove is formed to be a shape tapered toward the back to thereby facilitate the fitting between the lock plate and the receiving groove.
The above lock mechanism switches between a lock state in which the relative rotation phase is constrained to the given phase and a lock release state in which the constraint is released. The switching between the lock state and the lock release state is performed by supplying and discharging operating oil to the receiving groove through flow paths connecting to the receiving groove to thereby allowing the lock plate to be ejected and retracted to and from the receiving groove. The switching from the lock state to the lock release state is performed based on, for example, the temperature, the rotation speed, the accelerator opening degree of the engine and so on.
However, in the valve timing control apparatus disclosed in Reference 1, the lock plate is ejected from the outside toward the inside in the radial direction to be fitted to the receiving groove. Accordingly, even when the biasing force of the torsion spring acts on the lock plate in the lock state, there is a danger that the lock plate is retracted from the receiving groove unintentionally and that the lock is released in the case where the centrifugal force generated by the rotation of the engine is higher than the biasing force.
Additionally, as the end portion of the lock plate has the tapered shape, an external force in a retracting direction may act on the lock plate due to the backlash between the outer rotor and the inner rotor occurring in a state where hydraulic pressure is not sufficient such as at the time of starting the engine. As a result, there is a danger that the lock plate is retracted from the receiving groove and that the lock is released even though the centrifugal force higher than the biasing force of the torsion spring does not occur.
Furthermore, as the related-art valve timing control apparatus, there is the one in which ejecting and retracting direction of the lock plate is set to a direction parallel to a camshaft. In such valve timing control apparatus, there is the one in which the end portion of the lock plate is deformed to a tapered shape due to abrasion or the one in which the end is processed to be the tapered shape in advance so as to facilitate the ejecting and retracting to and from the receiving groove. Also in these valve timing control apparatus, there is a danger that a component force in the retracting direction acts on the lock plate due to the backlash between the outer rotor and the inner rotor occurring at the time of starting the engine and that the lock plate is retracted unintentionally to be in the lock release state.